The present invention relates to optical fiber network device technology and, more particularly, to devices which can split light signals responsive to the polarization of the light signals.
In modern fiberoptic telecommunications, more and more reliance is being placed on the state of polarization of light signals. Typically the polarization of the signal is used to help direct the signal along the fiberoptic network. Network components or devices which function based upon the polarization of light signals include fiberoptic polarization tunable filters, depolarizers, binary polarization switch/modulators, polarization division multiplexers and many other polarization related fiberoptic components. Many, if not all, of these devices require fiberoptic polarization beam splitters (PBSs). For example, devices using PBSs are described in U.S. appln. Ser. No. 08/406,212 entitled, "VARIABLE POLARIZATION BEAM SPLITTER, COMBINER AND MIXER", filed Feb. 22, 1995 by J. J. Pan and assigned to the present assignee.
A conventional polarization beam splitter cube, a pair of right angle prisms, is often used for its polarization beam splitting functions. The face of the hypotenuse of one prism is bonded to the hypotenuse face of the second prism with special dielectric materials to form a polarizing beam splitter cube with an internal interface at an angle 45.degree. to the external faces of the cube. Incoming light which travels perpendicularly to one of the external faces is refracted through the interface or reflected at the interface 90.degree. to the incoming light according to the polarization of the light. Light which is linearly polarized in the plane of incidence is transmitted through the cube. Light which is linearly polarized perpendicularly to the plane of incidence is reflected by the cube. However, the polarization beam splitter cube cannot handle signals at high power, which is desirable in modem applications.
Another type of polarization beam splitter is the Glan-Laser PBS in which two right angle prisms of birefringent crystals are used. The face of the hypotenuse of one prism is separated slightly from the hypotenuse face of the second prism. The Glan-Laser PBS is capable of handling high-power signals, but the shape of the light beams reflected from the cube are distorted. This distortion can cause undesirable effects upon the PBS and makes the Glan-laser PBS unsuitable in some applications.
The present invention also solves or substantially mitigates these problems by providing for a PBS which is capable of handling high-power signals without distortion of either the reflected and refracted signals. Furthermore, the PBS is adaptable for miniaturization as an element in fiberoptic network devices.